 | Acta Crystallographica Section D Acta Crystallographica Section D BIOLOGICAL CRYSTALLOGRAPHY |
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![[Figure 5]](fw5024fig5mag.jpg)
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Figure 5
Intersubunit interactions of AVR4. (a) Schematic presentation of the quaternary structure of avidin, AVR4 and streptavidin. The ribbon diagram (top) is depicted from the avidin coordinates and the cartoon (bottom) represents the relative arrangement of the monomers (numbered) in all three proteins. The tetramer on the right is rotated clockwise by 90° along the vertical axis. The intimate interaction of the 1–4 (and 2–3) monomer–monomer interface is clearly visible in the figure on the left. The contact surface of the alternative interface, comprising the dimer–dimer interaction (right), is much less extensive. (b) The 1–3 interface of avidin (magenta), AVR4 (cyan) and streptavidin (gold). The intersubunit interactions involve only three residues in avidin and streptavidin, although their character is somewhat different (e.g. the interaction in avidin is more hydrophobic than that of streptavidin). In contrast, the 1–3 contact surface of AVR4 contains the additional contribution of a fourth amino-acid side chain (Lys92), which crosses over from one monomer and forms a hydrogen-bonding interaction with Tyr115 of the other. (c) Close-up stereoview of the intricate hydrogen-bonding network between Lys92 and Tyr115 in the 1–3 monomer–monomer interface. The different subunits are coloured cyan and blue, respectively. The two Tyr115 from the different monomers form a π−π charge-transfer interaction with an angle of rotation of ∼60° between the two rings. Lys92 of the neighbouring subunit forms a hydrogen-bonding interaction with Tyr115, which increases the 1–3 contact surface. In addition, Lys92 forms two additional hydrogen-bonding interactions with Asn117 and a solvent molecule. |
![[Figure 5]](fw5024fig5.jpg)
| BIOLOGICAL CRYSTALLOGRAPHY |
ISSN: 1399-0047
